Electric terminal strips are commonly mounted on electric panels to provide a series of spaced terminals that facilitate wiring connections with external apparatus, as well as tracing the circuits on the panel. Electric terminal strips formed of modular terminal connector blocks are well known and are frequently used to provide the exact number of terminals required for the specific circuit on a panel. As a circuit modifications are frequently made to circuits previously wired on a panel, it is desirable that such terminal strips be assembled from individual, non-interlocking terminal blocks which are mounted upon a common track so that the number of terminal blocks on the track may be easily changed and additional blocks added to the assembly after the terminal strip is installed on a panel. Thus a need exists for a terminal block which can be installed or removed from a mounting track preferably without resorting to a tool using judicious prying pressure and which has a construction which will clearly visually indicate when the individual blocks are improperly mounted on the track.